The Canon NP-E3 Battery Pack discharge/complete recharge cycle done on the Canon charger takes about
8.5 hours for the discharge cycle plus about 2 hours for a complete charge.
Overnight is a good time to do this - 10.5 hours is a long time.

Chuck Westfall also adds further advice for professionals -
a professional generally meeting the following profile:
Owns 2 or 3 batteries, uses their camera at least 5 days per week
and averages at least 1,000 shots per week.
The Canon NP-E3 Battery Pack maintenance recommendation for a professional
is to recondition each battery about once per month after the initial conditioning.

Chuck also stresses that this is a guideline - not a requirement.
Individual shooting styles may dictate adjustment from this recommendation.

My recommendation is to have at least two Canon NP-E3 Battery Packs.
Keep one in the camera until fully drained,
keep the other(s) fully charged in your bag - ready for immediate use.
You are basically giving each battery a complete discharge/charge cycle during each use.

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